1. Field of the Invention
The present invention relates generally to inspection apparatus and, more particularly, is directed to a bottle or container inspection apparatus that detects a flaw such as a blowhole, blister or the like existing in the wall of a transparent type container.
2. Description of the Prior Art
In the recent years, plastic containers that are made of plastic materials such as polyethylene, etc., have become used as preservation containers for liquors, beverages or seasonings by substituting glass containers. Such containers feature easier massproduction, and are light weight and lower costing with the additional merit that breakage cautions like in the case of glass bottle are not necessary. However, a precaution point upon producing such containers is the prevention of flaws such as blowhole, blister, bubbles or the like flaw within the container wall.
Plastic containers are mainly produced by blow moulding methods whereas cases that air bubbles get mixed into the material may be relatively high. By moulding containers with materials containing air bubbles or by the mixture of air bubbles into the material during the moulding process, the formed product or container will carry a residual air bubble that is thinly compressed into its walls which are apt to cause the wall tear or damage at such wall portion with blister during usage or transit.
The detection of such extremely thin and minute blister extistence within the container's thin wall can be a very difficult task by the human vision.
FIG. 1 schematically shows one example of the main portions of a blister inspection apparatus according to the conventional art. In this example, the light from a light source 1 is irradiated onto a container 3 via a light diffuser plate 2, whereas a video camera 4 at the opposite side of container 3 in relation to the light source 1, receiver the light passing through the container, and then the video signal from the camera 4 is processed to inspect the existence or not of defects in the container 3.
However, in relations to the blisters within the container 3 walls, the contrast difference of brightness between the portions containing the blisters and none is extremely subtle to an extent that it was impossible to steadily and positively detect blister extistences by the conventional apparatuses.
In other wards, with the conventional inspection apparatus, while it was possible to detect the exsistences of opaque foreign particle such as stones or the like in the walls of container 3, it was very difficult to detect the existence of minute blisters within the walls. Further, by attempts to detect the existence of such minute blisters within the walls, since the contrast difference is subtle as mentioned above, at the conventional apparatus, it required complex image processing in order to boost such contrast difference. Further, it is incidental to such measure that the S/N (Signal to Noise) ratio detoriorates to an extent that the blister detection lacks stability so that the practical status was that such apparatus were not suitable for actual use.